A Guide to Avoiding AC and Furnace Maintenance Missteps

It happens to all of us: we move into our first place and realize there's more to adulting than buying our own groceries. Whether you're a first-time homebuyer or renting your first apartment, there's much to learn about maintaining your own household – not the least of which is AC maintenance and the effects dirty air filters can have on your AC. We're here to help by tackling some of the HVAC maintenance and air filter questions you might have.

Residential HVAC Questions

First, let's answer the big one: is an AC filter the same thing as a furnace filter? The answer is yes. It can be confusing when you do an internet search for one and the other pops up as an option, so it helps to know that they're basically interchangeable. The more important things to search for are the size you need and the MERV rating that will work best for your lifestyle. Once you figure out those basics, you can move on to the more in-depth questions about AC maintenance.

Dirty AC Filter Troubleshooting

 Is there a wrong way to put in an air filter?

Yes, there is definitely a wrong way to insert your air filter. On the side of your filter, you'll notice at least one arrow, possibly more – all pointing in the same direction. You'll want to make sure those arrows are pointing into the duct. For easy step-by-step instructions on changing your air filter, be sure to check out this Helpful Tip. Wondering if your HVAC unit is running properly? Read more about the problems that can arise and what happens if the air filter is backwards below.

 What happens if the air filter is backwards?

Inserting your air filter facing the wrong direction can cause a couple of problems for your system.

• The filter will have a difficult time doing its job. Air is meant to flow through the filter in a specific direction in order to best capture the dust and other pollutants that could clog your system.
• The filter may actually impede the flow of air into your system, making it work harder to circulate the air in your home – possibly leading to higher utility bills and even wearing out your unit faster.

 Is running the AC without a filter bad?

Technically, you can run your air conditioner or furnace without an air filter, but it's a bad idea. The filter's purpose is to remove dirt, dust, and other contaminants from the air as it moves toward the unit. If there is no filtration, those things can build up in your system and cause big problems, including shortening the life of the unit. You’ll also run into issues that arise from dirty air ducts which can affect your home wellness and even have detrimental effects on those with allergies and asthma. We recommend never running the AC without a filter.

 What happens if you don't clean an air filter?

If you're using a disposable filter, you don't have to clean it. You just need to replace it every 30-90 days – again, how often depends on your household and the efficiency (MERV rating) of the filter. If you’re unsure if your it’s time to replace a dirty AC filter, it’s best to err on the side of caution, especially if you have pets that bring in allergens, or if someone in the household experiences asthma or allergy symptoms. Dirty AC filters can also lead to higher energy bills since your unit has to work harder which can also end up affecting the longevity of your HVAC (which can be very costly to replace!).

 Can you put a wet filter in your air conditioner?

So, you have a washable filter, and you just cleaned it? Now what? Wait for it to dry completely before you put it back in its place. You may be tempted to cut corners or be in a hurry but putting a wet filter back can lead to mold growth in the filter. Obviously, mold is not something you want circulating throughout your home. It's safer to wait until the filter is completely dry.

 Can a dirty AC filter make your HVAC not work?

Whether you have an air conditioner or a furnace, replacing your filter regularly is one of the most important things you can do to keep your system running efficiently. If you run your air conditioner with a dirty air filter, the coils in it could become frozen, causing the system to run for longer periods of time and encouraging mold growth. Not changing the air filter for an extended period could decrease the life of your unit by up to half! Why risk it? Set yourself up for success by having your favorite filters on-hand and ready to go when it's time to replace a dirty one.

 Do air conditioners take in air from outside?

A common misconception is that air conditioners take in air from outside – likely because in split systems the AC unit sits outside the home. However, air conditioners do not take in air from outside, and there is usually an indoor and outdoor component that is connected by lines containing a refrigerant. The inside component of the air conditioning pulls in air through an indoor air intake grille which is where your air filter sits. As the air is pulled in, it passes through the cooled coils and pushes the cold filtered air back into your home.

 Why does my central air have two filters?

There are a few scenarios where multiple air filters are needed. Here are some cases which will require you to purchase air filters for two locations.

First, you may have multiple air intake ducts or multiple central air systems. If you live in a large enough home, you will probably have multiple air intake ducts so that air can properly be circulated and to maintain consistent temperatures throughout the home. For example, a multi-story home may be hotter on the second floor and cooler downstairs and there might be separate central air systems, causing each to have its own filters.

Some homes or workshops have an air handler. Air handlers typically have a thicker air filter depth and they can hold more pollutants and contaminants, meaning they won’t need to be changed as frequently as a return vent air filter.

 Do window air conditioner units have a filter?

Yes, window air conditioner units do have a filter and it’s important to clean or replace it on a monthly basis if the unit is running frequently. The air filter on a window unit would be located inside under the air intake grill. Note that not all units use the same kinds of air filters as a home HVAC system, check your unit and size requirements before purchasing air filters.

These are just a handful of common HVAC questions about maintenance and the dirty AC filter problems that can arise and you may experience more issues. We've probably answered most questions and more in our Helpful Tips section. Check it out to learn all you can about keeping your air conditioner or furnace in top condition, mitigating common allergies, and keeping the air you breathe at home clean and healthy.